“Sodium and water” experiment

Pieces of sodium rapidly run on water

Can we make met­al run across wa­ter? Let’s find out!

Safe­ty pre­cau­tions

Only work in pro­tec­tive gloves, glass­es and a mask. Ob­serve safe­ty rules when work­ing with flame and flammable ob­jects, and when work­ing with ac­tive met­als such as lithi­um, sodi­um, potas­si­um, ru­bid­i­um and ce­sium.

Reagents and equip­ment:

  • metal­lic sodi­um;
  • 1% sol. phe­nolph­thalein4
  • 1% sol. in­di­go carmine;
  • 1% sol. thy­mol blue;
  • wa­ter;
  • glass bowls

Step-by-step in­struc­tions

Pour wa­ter into the glass bowls, then add the in­di­ca­tor so­lu­tions – phe­nolph­thalein to the first, in­di­go carmine to the sec­ond and thy­mol blue to the third. Add a piece of metal­lic sodi­um. Watch the change of col­or in all three bowls.

Pro­cess­es de­scrip­tion

Sodi­um is a very re­ac­tive met­al, and can force hy­dro­gen out of wa­ter. When wa­ter makes con­tact with sodi­um the re­ac­tion of­ten takes place with an ex­plo­sion.

If you throw a small piece of sodi­um into a bowl of wa­ter con­tain­ing an acid base in­di­ca­tor, you’ll see an im­pres­sive ef­fect: the sodi­um starts to speed across the sur­face, and it also dis­solves, form­ing a bead which can even ig­nite, turn­ing into a fiery ball!

Why does sodi­um run

When it re­acts with wa­ter, hy­dro­gen is re­leased, which makes the sodi­um start “run­ning”.

Why does sodi­um dis­solve and ig­nite

The re­ac­tion of sodi­um with wa­ter takes place with an enor­mous re­lease of heat, which is suf­fi­cient to melt met­al and turn it into a bead, which is ac­tu­al­ly a ball of dis­solved met­al. Ad­di­tion­al­ly, the en­er­gy of this re­ac­tion is suf­fi­cient to ig­nite the hy­dro­gen re­leased!

Why does the col­or in the bowls change

Phe­nolph­thalein, in­di­go carmine and thy­mol blue are acid base in­di­ca­tors, i.e. sub­stances that change their col­or when the hy­dro­gen in­dex of the medi­um changes. When sodi­um re­acts with wa­ter, sodi­um hy­drox­ide is formed, which is a very strong base, and the medi­um be­comes al­ka­line. In­di­ca­tors change their col­or in the fol­low­ing way: phe­nolph­thalein from col­or­less to crim­son, in­di­go carmine from blue to green, and thy­mol blue from yel­low to blue:

2Na + 2H₂O = 2NaOH + H₂